classifier: Use fat_rwlock instead of ovs_rwlock.

classifier: Use fat_rwlock instead of ovs_rwlock.

Jarno Rajahalme reported up to 40% performance gain on netperf TCP_CRR with
an earlier version of this patch in combination with a kernel NUMA patch,
together with a reduction in variance:
    http://openvswitch.org/pipermail/dev/2014-January/035867.html

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>